Innovations in Degradable Polymers

why aren’t most research articles pursued by industry?

• not economical

• takes many years to implement on industrial scale

what does catalytic chemical recycling of post-consumer polyethylene start with?

post-consumer water jug (shred it)

steps of catalytic chemical recycling of post-consumer polyethylene

1. react shredded water drug w dehydrogenation catalyst → 0.5% of C-C backbone bonds dehydrogenated to C=C w/o change in MW

2.  cross-metathesis w 2-hydroxyethyl acrylate → MW goes down (chains breaking)

3. hydrogenation of C=C bonds

4. transesterification with diethanolamine (8% reacts)

5. repolymerization w MW = 80kDa → tensile strength now similar to og HDPE

6. depolymerization w ethylene glycol and triazabicyclodecene (TBD) → once recycled to monomer, can be repolymerized

step 1 of catalytic chemical recycling of post-consumer polyethylene

• react shredded water drug with dehydrogenation catalyst

• approximately 0.5% of C-C backbone bonds dehydrogenated to C=C double bonds without a change in MW

• essentially installing double bonds/unsaturated units without breaking polymer

step 2 of catalytic chemical recycling of post-consumer polyethylene

• cross-metathesis with 2-hydroxyethyl acrylate (cheap)

• essentially switch partners of double bond, adding new endgroup (breaking polymer chains in the process)

• results in ethylene byproduct

• end group = hydroxymethyl methyl methacrylate

• MW goes down quite a bit due to chains breaking

step 3 of catalytic chemical recycling of post-consumer polyethylene

• hydrogenztion of C=C bonds

• now only C-C single bonds

• repolymerization after this step made similar polymer Mn but much smaller Mw 

→ brittle & poor tensile behavior bc of lower Mw

step 4 of catalytic chemical recycling of post-consumer polyethylene

transesterification with diethanolamine (8% of hydrogenated material reacts)

step 5 of catalytic chemical recycling of post-consumer polyethylene

• repolymerization with Mw - 80 kDa

• tensile strength now similar to original HDPE

step 6 of catalytic chemical recycling of post-consumer polyethylene

• depolymerization with ethylene glycol and triazabicyclodecene (TBD)

• once chemical is recycled to monomer, can be repolymerized (circular)

cross metathesis

type of olefin metathesis rxn that involves the exchange of substituents b/w different olefins thru the breaking & reforming of C=C bonds

• catalyzed by metal complexes

transesterification

process of exchanging organic functional group of an ester with an alcohol

which new research innovation is a bottom-up approach?

chemically

bottom-up approach

synthesize monomer first and then polymerize/recycle it (start with a chemical reaction)

starting point for Chemically Recyclable Linear and Branched Polyethylenes

lactone

• a cyclic compound with an ester and an internal double bond

steps of Chemically Recyclable Linear and Branched Polyethylenes

1. ring open with methanol reflux & Sc catalyst (lewis acid accepts e- pair)

2. ring-opening metathesis polymerization w cyclooctenehydrogenate

3. Hydrogenation → yields telechelic monomers (2 different reactive end groups)

4. Transesterification for polymerization → no matter size of starting monomers, high MW polyethylene obtained

5. depolymerization by methanol reflux & Sc catalyst 

what is required for branched polymerization via Chemically Recyclable Linear and Branched Polyethylenes?

trifunctional monomer

step 1 of Chemically Recyclable Linear and Branched Polyethylenes

• ring open w methanol reflux & Sc catalyst

• Sc catalyst = lewis acid that accepts an electon pair, making C more electrophilic

step 2 of Chemically Recyclable Linear and Branched Polyethylenes

ring opening metathesis polymerization with cyclooctene

step 3 of Chemically Recyclable Linear and Branched Polyethylenes

• hydrogenation

• Mn was selected in the range b/w 2-16 kDa

• yields telechelic monomers (2 diff reactive end groups)

• A reacts w B on another monomer

telechelic monomers

type of polymer that has reactive groups located at both ends of linear structure

step 4 of Chemically Recyclable Linear and Branched Polyethylenes

• transesterification for polymerization

• no matter size of starting monomers, high MW polyethylene obtained (~100kDa)

step 5 of Chemically Recyclable Linear and Branched Polyethylenes

• depolymerization by methanol reflux & Sc catalyst

• can do branched polymerization with a trifunctional monomer

which approach starts with a system known to be easily chemically recycled?

Chemically Recyclable Thermoplastics from Cyclic Acetals

what polymer is known to be easily chemically recycled and used in Chemically Recyclable Thermoplastics from Cyclic Acetals?

poly(acetals)

poly(acetals)

• easily recycled to monomer using trace acid and heat (<150C)

• liquid

• easily distilled off in high purity

• in the past, MW weren’t high enough to make useful materials

• high MW version has good tensile strength

the high MW version of poly(acetals) has good _______ strength

tensile

pros of poly(1,3-dioxoiane) - a chemically recyclable thermoplastic

• tough thermoplastic

• thermally stable to 325 C

• monomer recovered in 98% yeield

• synthesized from inexpensive monomer w bio-sourcing options

• rapidly polymerized

describe use of RD-CROP of cyclic acetals

1. start with dormant species with X group

2. MOMBr adds Br to end of growing polymer chain forming active species

3. Br stabilizes and allows high MW to be reached with high control

4. monomer addition

5. cycles back to dormant species

the stress-strain curve for PDXL is very similar to which commercial polymer?

iPP = isotactic poly(propylene)

triggered depolymerization enables…

chemical recycling to monomer

steps of triggered depolymerization → chemical recycling in Chemically Recyclable Thermoplastics from Cyclic Acetals

1. collect polymer

2. add acid, heat to 140-150

3. distill

4. recover monomer

can pure DXL be recovered from mixed waste stream?

yes

• 96% recovery